I don't think any Public Body should be taking items such as Matalan Memberships or Magazine Subscriptions as proof of address particularly at present when so many illegal immigrants are using sham marriages to stay in the UK.
As you say they almost turned you away because Keith didn't have his passport and good luck you got it all accepted OK. These sham marriages 99% of the time are between a non Brit EU citizen (ie legally resident in the UK) and a Rest of World citizen ie the person wishing to aquire UK residency through the marriage - if people have to wait for more official letters to be addressed to them then so be it.
If you want to post the location of the Registry Office here I will gladly report them to the authorities.